Leave it on: Study says night lighting won't harm children's eyesight

(WebMD) -- Parents who have been stumbling in the dark to their baby's crib or depriving their toddler of a comforting night-light in fear of damaging their little ones' eyesight may have nothing to worry about after all.

Two studies published in this week's issue of the journal Nature have found that night-lights in childhood don't seem to cause development of nearsightedness later in life.

The studies contradict a highly publicized study from last year, also published in Nature, in which researchers reported finding that infants and toddlers who slept with the lights on were more likely to develop nearsightedness, or myopia, later on.

"It created quite a stir in the scientific community and the lay press," said vision scientist Jane Gwiazda, Ph.D., referring to last year's study, which was conducted by researchers at the University of Pennsylvania Medical Center. "I think a lot of parents have turned out the lights, and I've heard from practicing clinicians that this is the main question they've received from parents since this appeared in May."

Gwiazda is also director of the children's vision laboratory at the New England College of Optometry in Boston, which has been collecting information on the visual development of children and has followed some children for as long as 24 years.

She and her colleagues wanted to reexamine the issue, so they asked 213 of the parents whether they had used night-lights or left the bedroom lights on when their children slept. Comparing the responses to data culled over the years, the researchers found that children who had slept with night lighting when they were under the age of 2 weren't more likely to develop myopia later on.

A team of Ohio State University researchers reached the same conclusion. They, too, were surprised to hear of a connection and decided to test it on their own cohort of 1,220 children, whom they were following for a 10-year study on eye development. They found the rates of myopia to be "remarkably uniform" between the groups that were exposed to nighttime light and those who weren't, according to Karla Zadnik, D.O., Ph.D., associate professor in the university's college of optometry.

Still, the authors of the study that kicked off the controversy are not ready to concede.

"I think it raises more questions," said Richard Stone M.D., a pediatric ophthalmologist at the University of Pennsylvania Medical Center's Scheie Eye Institute, who will present more research data at an upcoming vision research conference in July. .

Intrigued by animal studies suggesting that round-the-clock lighting affected eye development in animals, Stone and his colleagues asked the parents of 479 patients about the nighttime lighting in their children's bedrooms. They found that 55 percent of children who slept in a room with the lights on later became nearsighted. The figure was 34 percent for those who used a night-light, but just 10 percent for children who slept in the dark.

Stone acknowledged that his subjects were drawn from a pool of patients who had come to the university for specialty eye care and may not represent the general population. And his study didn't take into account whether myopic parents tend to leave lights on more often than those with normal eyesight.

Gwiazda's team found that children of nearsighted parents were more likely to be nearsighted themselves, and that such parents were also more likely to leave the lights on, presumably to keep them from stumbling around in their children's rooms.

Stone suggested there might be a small subset of children who may be especially vulnerable to night-lights. And the National Eye Institute, an arm of the National Institutes of Health that helped pay for the two new studies, issued a statement saying it is too early to draw any conclusions one way or the other.

But pediatricians, who were skeptical of the earlier findings all along, say they are not telling parents to turn off the lights, especially night-lights, which can help calm a toddler who wakes up scared in the middle of the night.

"I've been in pediatrics for 20 years, and surely if there was something that was valid and was significant, it would have shown up by now," said Suzanne Corrigan, M.D., a pediatrician in Irving, Texas, and a spokeswoman for the American Academy of Pediatrics. "The night-light is just a friend. And they help the moms get to their babies without turning on a bright light."